uBlock

NOTE: this is the new main home for the uBlock extension.
A blocker designed for efficiency.
Though it has a low memory and CPU footprint, uBlock yet can load and enforce thousands of filters more than other popular blockers.
uBlock is more than an "ad-blocker": not only does it come with various built-in lists for blocking ads and protecting your privacy, but it also supports flexible customization — from adding your own lists to powerful Dynamic Filtering and more.
https://chrismatic.io/ublock/